Gas turbine fuel atomizing system

ABSTRACT

A gas-coupled regenerative gas turbine engine includes an airassembled fuel atomizing nozzle in the combustion apparatus. Air is supplied to the nozzle by a positive-displacement pump driven by the engine. The pump has a relatively high ratio of clearance volume to displacement so that, at higher operating speeds of the engine, flow from the pump is blocked by the back pressure in the discharge line from the compressor of the engine. Thus air assist is available for starting and idling, but little energy is used by the pump at high power levels of the engine.

United States Patent Bracken, Jr. et al.

[54] GAS TURBINE FUEL ATOMIZING SYSTEM [72] Inventors: Joseph W.Bracken, Jr., Redford Twp.; Roger A. Davison; Glenn W. Thebert, both ofCarmel, all of [21] Appl. No.: 129,870

[151 3,688,497 1 Sept.5i, 1972 3,426,527 2/1969 OConnor ..60/39.743,224,195 12/1965 Walsh ..60/39.74 3,095,707 7/ 1963 Flanigan et a1..60/39.74 R

Primary Examiner-Carlton R. Croyle Assistant Examiner-Warren OlsenAttomey-Paul Fitzpatrick and Jean L. Carpenter [57] ABSTRACT Agas-coupled regenerative gas turbine engine includes an air-assembledfuel atomizing nozzle in the combustion apparatus. Air is supplied tothe nozzle by a positive-displacement pump driven by the engine.

(g1. ..60/39.74 R,F The pump has a relatively high ratio of clearance on e e s I s I I e a e no so Fleld of R, S, speeds of the g flow from thep p is by the back pressure in the discharge line from the [56]References C'ted compressor of the engine. Thus air assist is availableUNITED STATES p ATEN'IS for starting and idling, but little energy isused by the pump at high power levels of the engine. 3,581,493 6/1971Sweet et a1 ..60/39.74 R 2,635,425 4/1953 Thorpe et a1. ..60/39.74 3Claims, 4 Drawing Figures REGENERATOR GAS TURBINE FUEL ATOMIZING SYSTEMDESCRIPTION This invention is directed to an improved system forproviding air to an airassisted fuel atomizing nozzle of a gas turbinecombustion apparatus.

A typical gas turbine fuel nozzle depends upon flow of fuel underpressure through small ports of the nozzle to atomize the fuel. Thismode of atomization is quite satisfactory at high fuel flow rates buttends to become less effective at very low rates of fuel flow. Such flowrates of fuel flow are encountered in small gas turbine engines, andparticularly in regenerative engines under low power or idlingconditions.

One solution to this problem is to provide air under pressure slightlyhigher than that into which the fuel nozzle discharges to assist theatomization of the fuel by the air so supplied.

The supply of the air for atomization presents some problems to whichthe present invention is considered to be a solution superior to thosepreviously proposed. In this connection, U.S. Pat. No. 3,095,707 ofFlanigan et al., July 2, 1963, shows a fuel system for a gas turbineengine in which air to assist in fuel atomization is provided by apick-up from the engine compressor under normal operating conditions,but is supplied by an auxiliary motor-driven pump during startingof theengine.

According to this invention, the air to aid in fuel atomization, whichwill hereafter be called atomizing air for conciseness, is supplied by apump of a positivedisplacement type driven by the engine, the pump beingcharacterized by a relatively high clearance volume. This characteristicis so related to the characteristics of the engine that the pumpsupplies air for atomizing up to a desired level of operation, normallynear full speed operation, and above this point the pump idles with thedischarge blocked by the back pressure in the air line from the pump tothe fuel nozzle communicated from the engine compressor.

The principal objects of the invention are to improve the fuelatomization in gas turbine engines, to provide an improved air-assistedfuel atomizing system, to provide an improved pumping arrangement forsupplying air for fuel atomization, to provide a pump arrangement whichis effective at low speeds of operation of the engine but which absorbsvery little power during normal operation of the engine, and to providean efficient pumping arrangement for supplying atomizing air which neednot be decoupled from the engine but which absorbs very little powerwhen not needed.

The nature of the invention and its advantages will be clear to thoseskilled in the art from the succeeding description of the preferredembodiment of the invention and the accompanying drawings thereof.

FIG. 1 is a schematic diagram of a gas turbine engine embodying theinvention.

FIG. 2 is a graph of air flow from a preferred pump.

FIG. 3 is a graph illustrating the air pressure characteristics of theair pump and engine compressor.

FIG. 4 is a sectional view, taken along the axis of the cylinder, of adouble-acting piston type atomizing air pump cylinder.

The engine may be of any known type and may, for example, be similar toany of those shown in the following U.S. patents: Amann et al., U.S.Pat. No. 3,116,605, Jan. 7, 1964; Collman et al., U.S. Pat. No.3,267,674,

Aug. 23, 1966; and Bell, U.S. Pat. No. 3,490,746, Jan. 20, 1970. Such anengine includes a compressor 2 which discharges through an outlet 3 intoa regenerator 4 in which the compressed air is heated and from which itflows through conduit 6 to a combustion apparatus 7. The combustionapparatus may include an outer case 8 and a combustion liner 10. Themotive fluid is heated by combustion of fuel in the combustion liner andthe resulting combustion products are fed through a transition duct 11to a compressor-driving or gas generator turbine 12 which drivescompressor 2 through shafting 14. The exhaust from turbine 12 proceedsto a second or power turbine 15 which drives the output shaft 16. Theexhaust from the turbine 15 flows through ducting 18, the regenerator 4,and an exhaust line 19 to atmosphere.

The combustion apparatus 7 includes a fuel nozzle 20 from which the fuelis sprayed into the combustion liner 10. The fuel is supplied from anysuitable properly controlled source of fuel under pressure through afuel line 23 to the nozzle. Atomizing air is supplied to nozzle 20through an air line 23 from a pump 24. This pump has an atmospheric airintake indicated at 26 and is driven by the gas generator turbinethrough the reduction gearing and shafting indicated at 27.

The details of the fuel nozzle 20 are immaterial to this invention,which may be used with any suitable air assisted fuel nozzle. One suchnozzle is illustrated in Grundman U.S. Pat. No. 3,310,240, Mar. 21,1967. Others long have been commercially available. The pump 24 isindicated schematically in FIG. 1 as a piston type pump including acylinder 28, a piston 30, a crankshaft 31, and a connecting rod 32 bywhich the piston is reciprocated.

Because of its desirable characteristics for the system, the preferredtype pump is a double-acting positive displacement pump of the pistonand cylinder type. Such pumps are well known and the design of them isfully understood. Structure of a preferred type pump according to theinvention is further illustrated in FIG. 4. In FIG. 4, the cylinder 28is shown as being defined by two cast heads 34 and 35 suitably heldtogether in face to face relation and with a liner or bushing pilotedwithin the two heads and providing a surface against which the piston 30slides. The 34 and 35 34 are integral with webs 38 and 39 which aresuitably fixed to end plates 40 and 42 as by the cap screw 43 and othercap screws not illustrated. A wall 44, which extends from one plate 40to the other plate 42 and is fixed to the webs 38 and 39, defines withthem a compressed air discharge chamber or plenum .46 which enclosesabout half of the circumference of the cylinder 28. The piston 30 isfixed to a reciprocating piston rod 47 guided in the web 39 by a bushing48. This rod is suitably connected by a connecting rod (not illustrated)to a crank 31 so that the piston is reciprocated by the crank.Atmospheric air can enter the pump cylinder 28 from the space 26 throughconventional reed-type inlet valves 50, one on each head, and the air isexhausted from the cylinder through conventional reed-type outlet valves51 mounted on each cylinder head. The outlet valves discharge into theplenum 46 from which the air flows through the compressed air line 23 tothe fuel nozzle.

The air pump is driven off the accessory drive gearing of the gasturbine engine at a speed much reduced from that of the gas generatorturbine. In a particular pump adapted for use with an engine of about300 horsepower rating, the piston is 3% inches in diameter and thestroke is about six-tenths inch. The average clearance at the ends ofthe cylinders is also about sixtenths inch, so that the clearance volumeis quite large with respect to the displacement as compared to ordinaryexpansible chamber air pumps. The pump is thus effective up to a littlebetter than two to one compression ratio.

As illustrated in FIG. 3, the discharge pressure of the enginecompressor 2 rises from atmospheric at zero engine speed to a value ofabout three times atmospheric at full speed. The discharge pressure ofthe air pump rises rapidly at low pump speeds, and then slowly, andfinally levels off at slightly below 40 pounds per square inch absolute.Where the discharge pressure curve of the pump crosses the enginecompressor curve flow from the pump will cease because of the backpressure from the combustion chamber. As will be seen, the air pumpdischarge pressure is slightly higher than the engine compressordischarge pressure over a considerable range up to about 2,700 pumprevolutions per minute.

With the particular engine and nozzle for which the specific pumpdescribed was sized, an air flow of approximately li cubic feet perminute at 5 pounds per square inch above combustion chamber pressure isdesired for atomizing fuel at the lower engine speeds. The curve of FIG.2 shows that the pump output rises to the desired value at below 300pump rpm, which is below the point at which fuel is injected into theengine for starting. The capacity which rises to about 5 cubic feet perminute and then declines so that at approximately 2,700 rpm of the pumpthe flow ceases.

This pump characteristic could be obtained with a single-acting pump butthe double-acting pump is desirable since at the higher speeds thepiston oscillates in a mass-elastic system with the air beingalternately compressed and rarified on each side of the piston. Theresult is that there is very little energy imparted to the air, which issimply being cyclically expanded and compressed, and therefore notroublesome heating of the pump or loss of energy due to pumping losses.The pump may simply be air cooled and the energy requirement is small.It will be apparent, of course, that no air flow control or shutoffs,relief valves, or other such gear is required; that the system as awhole is both simple and reliable.

Because of the relatively large piston area of the pump, it is capableof supplying the needed air at quite low engine speed. On the otherhand, because of the high clearance volume, the energy input and airpressure do not increase to undesirable values at higher speeds.

It will be clear that various types of positive-displacement pumps maybe used, and that the invention is applicable to various gas turbinecycles.

The detailed description of preferred embodiments of the invention forthe purpose of explaining the principles thereof is not to be consideredas limiting or restricting the invention, as many modifications may bemade by the exercise of skill in the art.

lclaim: l. A gas turbine engine comprising a compressor,

combustion apparatus supplied by the compressor, a turbine energized bythe combustion apparatus and connected to drive the compressor, and afuel atomizing nozzle in the combustion apparatus supplying fuel to thecombustion apparatus, the fuel nozzle being of an air-aided type andincluding a fuel inlet and an air inlet, in combination with means forsupplying air to the said air inlet comprising an air pump of anexpansible-chamber type driven by the turbine, the pump having anatmospheric inlet and having a ratio of clearance volume to displacementsufficiently high that pump output is terminated by compressor dischargepressure above a predetermined turbine speed indicative of ability ofthe fuel nozzle to atomize fuel effectively without air assistance.

2. A gas turbine engine comprising a compressor, combustion apparatussupplied by the compressor, a turbine energized by the combustionapparatus and connected to drive the compressor, and a fuel atomizingnozzle in the combustion apparatus supplying fuel to the combustionapparatus, the fuel nozzle being of an air-aided type and including afuel inlet and an air inlet, in combination with means for supplying airto the said air inlet comprising an air pump of a positivedisplacementtype driven by the turbine, the pump having an atmospheric inlet andhaving a ratio of clearance volume to displacement sufficiently highthat pump output is terminated by compressor discharge pressure above apredetermined turbine speed indicative of ability of the fuel nozzle toatomize fuel effectively without air assistance.

3. A gas turbine engine comprising a compressor, combustion apparatussupplied by the compressor, a turbine energized by the combustionapparatus and connected to drive the compressor, and a fuel atomizingnozzle in the combustion apparatus supplying fuel to the combustionapparatus, the fuel nozzle being of an air-aided type and including afuel inlet and an air inlet, in combination with means for supplying airto the said air inlet comprising an air pump of a doubleactingpositive-displacement type driven by the turbine, the pump having anatmospheric inlet and having a ratio of clearance volume to displacementequal approximately to unity.

3 23 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent M3,688,497 Dated September 5, 1972 Joseph W.Bracken, Jr., Roger A.Davison, and lnventorts) enn W mien- It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

On the title sheet, addresses of the inventors should read Joseph W.Bracken, Jr., Redford Twp, Michigan;

Roger A. Davis and Glenn W. Thebert, both of Camel, Indiana In theAbstract, line 2, "air-assembled" should read air-assisted Column 2,line 48, before the numeral "34" insert heads line 49, delete thenumeral "'34" Signed and sealed this 13th day of February 1973.

(SEAL) Attest:

EDWARD N.FLETCI'IER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A gas turbine engine comprising a compressor, combustion apparatussupplied by the compressor, a turbine energized by the combustionapparatus and connected to drive the compressor, and a fuel atomizingnozzle in the combustion apparatus supplying fuel to the combustionapparatus, the fuel nozzle being of an airaided type and including afuel inlet and an air inlet, in combination with means for supplying airto the said air inlet comprising an air pump of an expansible-chambertype driven by the turbine, the pump having an atmospheric inlet andhaving a ratio of clearance volume to displacement suffiCiently highthat pump output is terminated by compressor discharge pressure above apredetermined turbine speed indicative of ability of the fuel nozzle toatomize fuel effectively without air assistance.
 2. A gas turbine enginecomprising a compressor, combustion apparatus supplied by thecompressor, a turbine energized by the combustion apparatus andconnected to drive the compressor, and a fuel atomizing nozzle in thecombustion apparatus supplying fuel to the combustion apparatus, thefuel nozzle being of an air-aided type and including a fuel inlet and anair inlet, in combination with means for supplying air to the said airinlet comprising an air pump of a positive-displacement type driven bythe turbine, the pump having an atmospheric inlet and having a ratio ofclearance volume to displacement sufficiently high that pump output isterminated by compressor discharge pressure above a predeterminedturbine speed indicative of ability of the fuel nozzle to atomize fueleffectively without air assistance.
 3. A gas turbine engine comprising acompressor, combustion apparatus supplied by the compressor, a turbineenergized by the combustion apparatus and connected to drive thecompressor, and a fuel atomizing nozzle in the combustion apparatussupplying fuel to the combustion apparatus, the fuel nozzle being of anair-aided type and including a fuel inlet and an air inlet, incombination with means for supplying air to the said air inletcomprising an air pump of a double-acting positive-displacement typedriven by the turbine, the pump having an atmospheric inlet and having aratio of clearance volume to displacement equal approximately to unity.